I know Facebook (or twitter) will never do it, but Facebook really needs a 'Mark as read' feature for posts that you have already read. If there is an update or a new comment on the post that you have already read, it can go 'unread'.
This way the same post doesn't have to keep popping up in my news feed. It needs to be like Email Conversation - 'Mark as read' till you get a new response to the conversation. And you can have further refinement for public page posts where random people keep on commenting, that says 'Mark as read forever'.
Ofcourse this goes against Facebook's idea of making money - by keeping people on their site all the time. So its not going to happen, and who wants to see an 'empty news feed page'. It will be so depressing for people. "Oh! nothing more to read or follow? I have no friends, I have no life! What do I do with my life now".
Something like a news reader (reader.google.com is dead. I am so sad, I used to love it) where you know you have read everything you wanted to, now move on to things that are more important in life.